So the thought kinda hit me and I think the answer may be yes I wanna get opinions on this.
So for those who arent aware, idler pulleys/bearings force the belt into a path that engages more teeth, making torque transfer better and helps prevent belt slippage from loose belts.
So my question is, when installing an idler pulley, should you mount it on the top or bottom portion of the belt? Both will increase the number of engaged teeth on the motor pulley but, and here’s where I dont quite know how to quantify the feeling, that placing on the top section of the belt, the portion that is under tension, would reduce the life of the belt from excess wear.
So my reasoning is on a idler pulley free set up, the top portion of the belt in under tension but is straight, meaning the tension balances itself out in regards to the set up. (two forces in equal and opposite directions). But when you introduce an idler pulley on the top portion, you get an imbalance that the pulley must make up for. You have two equal forces at an angle to each other and the balancing force is applies to the belt by the idler pulley. The point should balance out to a zero sum in a free body diagram of that point on the belt. This means there’s more wear on the backside of the belt, which is going to happen due to the contact but I think that can be minimized.
I think if you place the idler pulley on the bottom portion of the motor mount and engage the lower portion of the belt that is not under tension, and is also not under compression because belts, chains and ropes cannot be put under compression, they fold. I think you can significantly reduce the wear and tear on the exterior portion of the belt exploiting this fact.
Slight disclaimer, the forces experience by the belt are actually not equal and but are opposite. There is a net force in the direction of travel which is why the belt rotates under the motors applied toque but I’m ignoring that for the purposes of making this easier to think about conceptually.
No Idler Pulley Where both forces are equal and opposite on one axis, no external wear resulting.
Top Side Idler Pulley Where A+A+B = 0 in a vector summation. bottom portion is still not under tension.
Bottom Side Idler Pulley Where a+b+c=0 but the magnitude of the tension is significantly less - just enough to change the path of the belt but no more - than that of the top portion of the belt, which is the driving portion of the belt. Because belts cannot be under compression.
This of course doesnt account for braking in which the tension switched from top to bottom but assuming we spend most of the time cruising rather than breaking I think the theory still holds. You can of course set the belt tension so high that in these examples, the lower portion of the belt is already under tension and instead of not being under tension during use, it simply lowers the magnitude of the tension on the bottom side but even then it still proves the point.